Production of cellulose



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Patented Feb. 9, 1954 UNITED STATES PATENT OFFICE PRDDUCTION F CELLULOSEN0 Drawing. Application April 27, 1950, Serial No. 158,594

Claims priority, application Great Britain May 27, 1949 11 Claims. 1

This invention relates to the production of cellulose from naturallyoccurring materials containing it.

It ha been proposed to obtain cellulose from ligno-cellulosic material,in particular wood, by heating the material with a concentrated aqueoussolution of chloracetic acid; a large proportion of the non-cellulosicconstituents of the material oes into solution in the aqueouschloracetic acid, and a fairly pure form of cellulose can be separatedby filtration and washing.

This process however has certain disadvantages. For one thing, a seriousamount of corrosion of the reaction vessel may occur; for another,

it is difficult to produce successive batches of cellulose havingsubstantially the same properties, even from the same stock of Wood,when using recovered chloracetic acid; for another, the amount ofchloracetic aci recoverable is unduly specially having regard to the hiost o this reagent t is an object of the present invention to overcomethese disadvantages.

We have found that a .major Iactor giving rise to each of thesedisadvantages is hydrolysi of the chlorace'tic acid, resulting in theliberation of free hydrochloric acid. We have also found that the amountof such hydrolysi c r ng can e very greatly reduced, or even renderednegligible, and a good yield of cellulo of a satisfactory degree ofpurity can still be obtained, if the chloracetic acid is dis olved in ordiluted with a substantially anhydrous organic substance which does notreact with it at the treatment temperature and which, a l ast at thetreatment temperature, forms with the chloracetic acid. a single liquidphase. If desired the chloracetic acid can be replaced by anotherchlorinated lower fatty acid, but generally speaking chloracetic acid isthe most convenient and cheapest chlorinated lower fatty acid to use,and its use is preferred. The term lower fatty acid is employed todenote fatty acids containing not more than 4 carbon atoms.

According to the invention therefore cellulose is produced froml-igno-cellulosic material by a process which comprises heating thematerial with a substantiall anhydrous homogeneous liquid mixture of achlorinated lower fatty acid, preferably oh loracetic acid, and anorganic substance which does not react with it.

The ligno-cellulos c mat rial may be employed in the ordinary air-drystate, and th exp ession substantially anhydrou mixture as applied tothe treating mixture includes mixtures contain might be derived from theligno-cellulosic material.

The organic substance with which the chlorinated fatty acid is mixed maybe regarded as either diluting or dissolving it (since most of thechlorinated fatty acids are solids at ordinary temperatures, thoughmolten at the treatment temperatures) but for the sake of convenience itwill be referred to in the present specification as a diluent; for thesame reason th invention will be described in more detail by referenceto the treatment of Wood with chloracetic acid, though it will beunderstood that the chloracetic acid can if desired be wholly or partlyreplaced by another chlorinated lower fatty acid, e. g, dichloraceticacid, trichloracetic acid, or one of the monoor di-chloropropionicacids, and that lignocellulosic materials other than wood can also betreated.

The diluent may be a low-boiling liquid such for instance as ethylacetate, acetone or chloroform, and as the treatment temperature willusually be above the normal boiling point of such a compound it willthen be necessary to carry out the treatment under pressure. We prefer,however, to use much higher boiling compounds, in particular compoundsof normal boiling point above about C. and advantageously between aboutand C. for instance hydrocarbons and hydrocarbon mixtures boiling withinthese limits, especially aromatic hydrocarbons containing 8 carbonatoms, normally liquid nitroand halogenated aromatic hydrocarbons, lowerfatty acids containing 2-4 carbon atoms, and fatty acid esters boilingat temperatures above 110 C. E);- amples of individual compounds whichgive very satisfactory results are Xylene (including 0-, m-, andp-xylcne and mixtures of two or more of these isomers) ethyl-benzene,nitrobenzene monochlorobenzene, acetic acid, propionic acid,

ethyl valerate or isovalerate and ethyl chlorac e Generally thechloracetic acid and the diluent will form a single liquid phase at alltemperatures between room temperature .(say about 15 C.) and thetreatment temperature. j

The relative proportions of the chloracetic acid and the diluent in themixture may vary over a cons derab r n e, ut i is e err d to cm ploymixtu es conta ni tween 5 and 85% by weight of chloracetic acid; withthe more resistant woods, e. g. spruce, the mixture may with inc such rlat v y s all mounts of Water as 65 advantage contain about 6570 80921of chloracetic acid, while with easily attacked woods, e. g. poplar,chloracetic acid contents down to 50% are very suitable. Advantageously,the wood may be treated with at least 3 times, and preferably 5 or moretimes, its weight of the mixture at a temume conditions, may however beadopted if desired. At temperatures of about l-ll0 C.

the treatment usually requires about 1-5 hours, depending in part onthenature of the wood being treated.

When the wood has been treated with the mixture of chloracetic acid anddiluent for the required time, the'resulting cellulose may be illteredoff as completely as possible and then washed, preferably with furtherquantities of the diluent or with acetone. Thus, when a mixture ofchloracetic acid and glacial acetic acid or xylene has been employed,the cellulose may be washed with further quantities of hot or coldglacial acetic acid or xylene (as the case may be) until little orsubstantially no chloracetic acid remains on the cellulose, after whichthe cellulose may be washed free from acid with water or from xylenewith a volatile organic solvent, e. g. acetone, alcohol, isopropyl etheror a low boiling hydrocarbon fraction consisting of hexanes with orwithout lower hydrocarbons. On the other hand, especially, but not only,when xylene or an ester has been used as the diluent, the cellulose maybe washed free from chloracetic acid with acetone, after which it may ifdesired be freed from acetone by heating it in a current of air.

After being washed, the cellulose may be heated for a short time with analkaline solution, preferably a caustic alkali solution of concentrationbetween 0.25% and 2%, to decompose any cellulose chloracetate that mayhave been formed, and may then, if desired, be given a bleach, e. g.with hypochlorite or sodium ch10 ,rite, and/or any other desiredpurification treatment, for example a treatment with alkali. Inparticular the bleached or unbleached cellulose, which is already of afairly high degree of purity, may be treated with a warm caustic sodasolution of concentration between 15% and 22%, as described in ourco-pending United States applications Ser. No. 75,963, filed 11thFebruary, 1949, now Patent No. 2,645,576, and Ser. No. 154,886, filedApril 8, 1950, now Patent No. 2,645,577, or the unbleached cellulose maybe given one of the other purification treatments referred to in UnitedStates application Ser. No. 75,963.

In order to recover the chloracetic acid'and diluent, the filtrateobtained after the main treatment, preferably together with the firstwash liquors, may be diluted with a fairly high proportion of alcohol orwater, preferably at room temperature or below, so as to precipitate thelignin, which may then be filtered off or otherwise separated. Thealcoholic or aqueous acid remaining may then be reconcentrated,preferably by a solvent extraction method carried out in the cold; forexample aqueous chloracetic and acetic acids may be concentrated byextraction with mixtures of ethyl acetate and benzene. In an alternativemethod the chloracetic acid and diluent (and the washing agent if thecellulose has been washed with a liquid other than the diluent, e. g.acetone) may be distilled directly from the filtrate, leaving theligning as residue. The later wash liquors contain little or nochloracetic acid or lignin, and may be treated to recover the diluent inany desired way. The chloracetic acid and the diluent recovered may beemployed in the treatment of further quantities of wood, theconcentration of the chloracetic acid in the mixture being adjusted asmay be desired or necessary.

While the new process is applicable to various types of ligno-cellulosicmaterial, including cereal straws and the residues of other annualplants, it is particularly useful and its advantages are most apparentin the treatment of woods, including both coniferous and deciduouswoods, for example, spruce, larch, fir, poplar and beech. It is foundthat the yields of cellulose obtained are very considerably greater, e.g., between about 13% and 20% greater depending on the type of woodtreated, than those obtained when pulping by a conventional alkali typeprocess such as the soda or sulphate process, following a dilute acidpre-hydrolysis; moreover, the quality of the cellulose obtained, asdetermined by its alpha-cellulose and pentosan contents and also by theclarity and viscosity of cellulose acetate made therefrom, is in manycases also higher.

The invention is illustrated by the followin examples:

Example 1 Spruce chips were added to 6 times their Weight of a mixtureof '75 parts by weight of chloracetic acid and 25 parts by weight ofglacial acetic acid, and the mixture boiled under reflux for 1% hours.The acid mixture was then separated from the cellulose by filtration asthoroughly as possible, and the cellulose washed first with acetic acidand then with water until it was free from acid; the acetic acidwashings were added to the original filtrate, the water washings beingkept separate. The cellulose was then bleached in two stages withhypochlorite, washed and fur ther treated with alkali to reduce itspentosan content. The purified cellulose had an alphacellulose contentof 98% and a pentosan content of 1.29%; on acetylation it gave acellulose acetate of viscosity 30 and clarity 41; the correspondingfigures for cellulose made from the same wood by a soda pulpingfollowing an acid prehydrolysis and purified in the same way were:alpha-cellulose content 93.2%, pentosan content 1.38%, cellulose acetateviscosity 1%, cellulose acetate clarity 14. The yield of purifiedcellulose was 37.6% compared with 33.2% by the soda process followingprehydrolysis. (The figures for viscosity and clarity are on anarbitrary scale and are given for purposes of comparison only.)

Example 2 Poplar chips were treated as described in Ex ample 1, exceptthat a 50:50 mixture of chloracetic and acetic acids was used, and theboiling was continued for 4 hours. The purified C611 followingprehydrolysis.

Example 3 Beech chips were treated as described in Example 1, exceptthat a 65:35 mixture of chloracetic and acetic acids was used, and theboiling was continued for 4 hours. The purified cellulose had analpha-cellulose content of 97.0% and a pentosan content of 1.81%. Theyield was 34.7% compared with 30.2% by the soda process followingprehydrolysis.

Example 4 Eucalyptus chips were boiled under refiux for 3 hours with 5times their weight of a mixture of equal parts by weight of chloraceticacid and xylene. The crude cellulose so obtained was separated byfiltration from as much of the treating mixture as possible, and wasthen washed with acetone until free from chloracetic acid, xylene andseparated lignin. (The washings, after removal of the acetone bydistillation, were added to the remainder of the separated treatingmixture for recovery and re-use of the chloracetic acid and xylene.) Thewashed cellulose was boiled at atmospheric pressure for 30 minutes witha 1 aqueous caustic soda solution and was then bleached in two stageswith hypochlorite and given a treatment with alkali to remove pentosans.The yield of purified cellulose was 41.1%.

Example 5 The process of Example 4 was repeated, except that the xylenewas replaced by ethyl chloracetate. The yield of crude cellulose (i. e.,after the boil with 1% caustic soda solution but before bleaching) was49.5%; a bleach with sodium chlorite reduced this to 46.4%. The bleachedcellulose, which had not been given a special pentosan-removing alkalitreatment, had an alpha-cellulose content of 89% and a pentosan contentof 3.95%.

Example 6 Wheat-straw was boiled for 4 hours with 8 times its weight ofa mixture of equal parts by weight of chloracetic and acetic acids. Theresulting cellulose was separated and washed as described in Example 1,and was then bleached with l'iypochlorite and given an alkali treatmentto reduce its pentosan content. The yield of unbleached cellulose was35.0%; the yield of bleached and purified cellulose was 31.0%, itsalpha-cellulose content being 96.0%, its pentosan content and itsmineral content 0.69%. If the straw, before being boiled with thechloracetic acid and acetic acid, was boiled first for 3 hours with a 1%hydrochloric acid solution and then for 2 hours with a 1% caustic sodasolution, the corresponding figures were: Yield (unbleached) 28.0%,(bleached and purified) 23.0%; analysis or purified cellulose:Alpha-cellulose 93.2%, pentosan 1.50%, mineral 0.40%.

Having described our invention, what we desire to secure by LettersPatent is:

1. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature between 120and 150 C. with an anhydrous homogeneous liquid mixture of a chlorinatedfatty acid containing up to three carbon atoms in the molecule and anorganic diluent inert to the chlorinated fatty acid, the concentrationof the chlorinated fatty acid in the mixture being 45-85% by weight.

2. Process for producing cellulose from lignocellulosic material,- whichcomprises heating ligno-cellulosic material to a temperature between 120and 150 C. with an anhydrous homogeneous liquid mixture ofmonochloracetic acid and an organic diluent inert to the monochloraceticacid, the concentration of the monochloracetic acid in the mixture being45-85% by weight.

3. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature of 125 440C. with an anhydrous homogeneous mixture of a chlorinated fatty acidcontaining up to three carbon atoms in the molecule and at least onenormally liquid saturated hydrocarbon of boiling point between 115 C.and 150 C., the concentration of the chlorinated fatty acid in themixture being 45-85% by weight.

4. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature of 115-149C. with an anhydrous homogeneous mixture of a chlorinated fatty acidcontaining up to three carbon atoms in the molecule and at least onearomatic hydrocarbon having the empirical formula CBHIO, theconcentration of the chlorinated fatty acid in the mixture being ail-%by weight.

5. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature of l25-1d0C. with an anhydrous homogeneous mixture of a chlorinated fatty acidcontaining up to three carton atoms in the molecule and a fatty acidcontaining 2-4. carbon atoms in the molecule, the concentration of thechlorinated fatty acid in the mixture being 45-85 by weight.

6. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature of 125-140C. with an anhydrous homogeneous mixture of a chlorinated fatty acidcontaining up to three carbon atoms in the molecule and acetic acid, theconcentration of the chlorinated fatty acid in the mixture being 45-85%by weight.

7. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature of l25-1i0C. with an anhydrous homogeneous mixture of a chlorinated fatty acidcontaining up to three carbon atoms in the molecule and an ester boilingbetween and 150 C. of an acid containing 2 to 5 carbon atoms, selectedfrom the group which consists of fatty acids and their chlorinesubstitution products, the concentration of the chlorinated fatty acidin the mixture being 45-85% by weight.

8. Process for producing cellulose from lignocellulosic material, whichcomprises heating ligno-cellulosic material to a temperature of -l l0 C.with an anhydrous homogeneous mixture of a chlorinated fatty acidcontaining up to three carbon atoms in the molecule and ethylmonochloracetate, the concentration of the chlorinated fatty acid in themixture being 45-85% by weight.

9. Process according to claim 1, wherein the cellulose produced iswashed substantially free from chlorinated fatty acid by means offurther quantities of the diluent.

10. Process according to claim 1, wherein the cellulose produced iswashed substantially free from chlorinated fatty acid by means ofacetone.

11. Process according to claim 2, wherein the cellulose produced isheated with an. alkaline 7 8 solution to saponify any cellulosechloracetate Number Name Date that may have been formed. 1,806,703 Ottet a1 May 26, 1931 STANLEY CHARLES BATE. 2,022,654 Dreyfus Dec. 3, 1935FRANCIS GEORGE PEACH. 2,061,616 Dreyfus NOV. 24, 1936 WALTER ALANROGERSON. 5 2,070,585 Dreyfus Feb. 16, 1937 2,538,457 Hudson Jan. 16,1951 References Cited. in the file of this patent UNITED STATES PATENTSOTHER REFERENCES Schutz: Chemical Abstracts, vol. 35, pp.

Number Name Date 10 4 3 49 7 3349 Smith 1343 Virasoro: ChemicalAbstracts, v01. 36, p. 6011. 117,134 Adamson July 18, 1 Wiltshire PaperInd. & Paper World, 1945,

962,173 Stark June 21, 1910 13 3

1. PROCESS FOR PRODUCING CELLULOSE FROM LIGNOCELLULOSE MATERIAL, WHICHCOMPRISES HEATING LIGNO-CELLULOSE MATERIAL TO A TEMPERATURE BETWEEN 120*AND 150* C. WITH AN ANHYDROUS HOMOGENEOUS LIQUID MIXTURE OF ACHLORINATED FATTY ACID CONTAINING UP TO THREE CARBON ATOMS IN THEMOLECULE AND AN ORGANIC DILUENT INERT TO THE CHLORINATED FATTY ACID, THECONCENTRATION OF THE CHLORINATED FATTY ACID IN THE MIXTURE BEING 45-85%BY WEIGHT.